Battery Absorbtion time with solar + wind

MatthewLynchMatthewLynch Registered Users Posts: 2
Hello, I currently have a solar instalation for aon off-grid micro grid. I have 12kW in solar panels and 1200Ah 48V battery bank. I also live in a very windy place (average wind is 9 m/s) so I have been considering a wind turbine to reduce the ammount of cycles or DOD on the batteries during the night or winter when we have very short days.

My concern is that all wind turbines I could find in my country they use a divert load to regulate. So when batteries reach a specified voltage it will dump the rest of the load. In summer days are very long and I will fully charge the batteries almost every day. The people selling the wind turbine said I should set the divert voltage slightly higher than the absorb voltage of the solar charger. So for my batteries (VRLA) the manual says 2.35V per cell with a -4mV/°C compensation. So for example the divert load would be set to 2.38V per cell. My concern is hoy much time the battery would be at this voltage. Currently my solar charger will do a 3hs absorb and switch to float. But taking into consideration in summer we have alot of sun and also alot of wind I don't want to damage our battery bank by having it at absorv voltage for several hours a day.

Will this damage the battery? or what should I do?



  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    edited July 6 #2
    Welcome to the forum Matthew,

    I am guessing you are somewhere in Argentina?

    It sounds like you have a good idea of how to setup and run the wind charging in combination with the solar charging system.

    Most basic wind charging systems work as you suggest... Wind turbine connected directly to battery bank with some sort of dump controller... Horizontal Axis Wind Turbines will over-speed in moderate to high winds (and can self destruct) without a load (battery bank) attached.

    There are integrated controllers of various types that can shutdown the turbine when the battery is full (brake, furl, feather, or "short" the turbine's alternator to load and "stall" the blades).

    I see you have posted a link to a DIY (do it yourself) dump controller in another thread in the forum:

    If you are looking to install wind on your property... Building your own turbine can be better than many you can purchase...

    9 m/s (20 mph) wind speed is very high/good... Is that "average" or peak for your area. Most turbines seem to need around 10-12 MPH to begin to harvest a "useful" amount of power, and >25 MPH many will start to reduce harvest or even shut down for safety.

    Turbines usually need around a 10-30+ meter tall tower to get into "clean air" (need to be above trees/buildings in area)...

    Midnite Solar makes some "interesting" systems for wind turbines. They uses their MPPT type charge controller to optimize energy harvest from turbines (MPPT allows the turbine to turn at "optimum" RPM based on wind and energy needs--MPPT can dramatically wind harvest--And integrated dump controller: and Hydro

    I don't know much about these systems... So others will have to supply that information (or contact the mfg/supplier).

    Do you have some hardware you are thinking of using/buying/building?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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